Fall detection using electronic devices is already known in the art. These are particularly widespread in the geriatric field, where it is often the case that a subject may fall and subsequently be unable to call for help. For example, U.S. Pat. No. 7,450,332 discloses an integrated free-fall detection device for a portable apparatus where an acceleration sensor generates acceleration signals correlated to the components of the acceleration of the portable apparatus along three detection axes, said device encompassing a dedicated purely hardware circuit connected to the acceleration sensor, which generates a free-fall detection signal in a continuous manner and in real-time. The free-fall detection signal has a first logic value in the event that the acceleration signals are simultaneously lower than a respective acceleration threshold, and this value is sent to a processor unit of the portable apparatus as an interrupt signal to activate the appropriate actions of protection for the portable apparatus.
In another example, European patent EP1870037 discloses a portable apparatus for detecting falls and immobility of a subject, comprising at least one sensor that generates a signal indicative of the accelerations of at least one portion of the subject's body, a control unit suitable for processing this signal and communication means for sending a call for help to a remote control station. The control unit may automatically activate the communication means only when a fall of the subject and his/her subsequent immobility are detected based on said processing. Typically in fall detection apparatus, as exemplified by EP1870037, a guard time timer is provided that ensures that the apparatus is immobile after a sudden change in movement. In this way, false positives that are created purely as a result of sharp or exaggerated movement are reduced.
Present fall detectors implementations are typically based on specific devices such as those described above to be fixed to the wrist or the hip, which include an accelerometer and run certain mathematical algorithms in order to determine whether a fall event has occurred.
Such portable electronic devices which are designed to be worn near the hip on a belt or a clip on the belt are considered to be the most reliable ones because the hip is generally less prone to sporadic movement than a subject's limbs. Nevertheless, they generally have to rely on an indication that the device is locked onto the hip and otherwise not to activate the fall detection algorithm. Others such portable electronic devices that are designed to be worn on the wrist, for example, on watches, generally provide a lower detection success rate and is accountable for more false positive results than devices designed to be worn near the hip because the device is not so close to the body's center of gravity and the movement is generally less stable.
A problem with the current techniques for detecting a fall event is that the percentage of successful fall detections is not adequately high and the percentage of false positive detections is not adequately low. A false positive detection may be understood as a positive detection event that has been triggered incorrectly, i.e. a positive output is given although a fall event has not actually occurred. It is therefore an object of the present invention to provide a method, system and device for detecting fall event with improved accuracy, offering high rate of successful fall detections and a low rate of false positive detections.